<?php
// This file is part of Moodle - http://moodle.org/
//
// Moodle is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// Moodle is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with Moodle.  If not, see <http://www.gnu.org/licenses/>.

/**
 * Mysql specific SQL code generator.
 *
 * @package    core_ddl
 * @copyright  1999 onwards Martin Dougiamas     http://dougiamas.com
 *             2001-3001 Eloy Lafuente (stronk7) http://contiento.com
 * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
 */

defined('MOODLE_INTERNAL') || die();

require_once($CFG->libdir.'/ddl/sql_generator.php');

/**
 * This class generate SQL code to be used against MySQL
 * It extends XMLDBgenerator so everything can be
 * overridden as needed to generate correct SQL.
 *
 * @property mysqli_native_moodle_database $mdb
 *
 * @package    core_ddl
 * @copyright  1999 onwards Martin Dougiamas     http://dougiamas.com
 *             2001-3001 Eloy Lafuente (stronk7) http://contiento.com
 * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
 */
class mysql_sql_generator extends sql_generator {

    // Only set values that are different from the defaults present in XMLDBgenerator

    /** @var string Used to quote names. */
    public $quote_string = '`';

    /** @var string To define the default to set for NOT NULLs CHARs without default (null=do nothing).*/
    public $default_for_char = '';

    /** @var bool To specify if the generator must use some DEFAULT clause to drop defaults.*/
    public $drop_default_value_required = true;

    /** @var string The DEFAULT clause required to drop defaults.*/
    public $drop_default_value = null;

    /** @var string To force primary key names to one string (null=no force).*/
    public $primary_key_name = '';

    /** @var string Template to drop PKs. 'TABLENAME' and 'KEYNAME' will be replaced from this template.*/
    public $drop_primary_key = 'ALTER TABLE TABLENAME DROP PRIMARY KEY';

    /** @var string Template to drop UKs. 'TABLENAME' and 'KEYNAME' will be replaced from this template.*/
    public $drop_unique_key = 'ALTER TABLE TABLENAME DROP KEY KEYNAME';

    /** @var string Template to drop FKs. 'TABLENAME' and 'KEYNAME' will be replaced from this template.*/
    public $drop_foreign_key = 'ALTER TABLE TABLENAME DROP FOREIGN KEY KEYNAME';

    /** @var bool True if the generator needs to add extra code to generate the sequence fields.*/
    public $sequence_extra_code = false;

    /** @var string The particular name for inline sequences in this generator.*/
    public $sequence_name = 'auto_increment';

    public $add_after_clause = true; // Does the generator need to add the after clause for fields

    /** @var string Characters to be used as concatenation operator.*/
    public $concat_character = null;

    /** @var string The SQL template to alter columns where the 'TABLENAME' and 'COLUMNSPECS' keywords are dynamically replaced.*/
    public $alter_column_sql = 'ALTER TABLE TABLENAME MODIFY COLUMN COLUMNSPECS';

    /** @var string SQL sentence to drop one index where 'TABLENAME', 'INDEXNAME' keywords are dynamically replaced.*/
    public $drop_index_sql = 'ALTER TABLE TABLENAME DROP INDEX INDEXNAME';

    /** @var string SQL sentence to rename one index where 'TABLENAME', 'OLDINDEXNAME' and 'NEWINDEXNAME' are dynamically replaced.*/
    public $rename_index_sql = null;

    /** @var string SQL sentence to rename one key 'TABLENAME', 'OLDKEYNAME' and 'NEWKEYNAME' are dynamically replaced.*/
    public $rename_key_sql = null;

    /** Maximum size of InnoDB row in Antelope file format */
    const ANTELOPE_MAX_ROW_SIZE = 8126;

    /**
     * Reset a sequence to the id field of a table.
     *
     * @param xmldb_table|string $table name of table or the table object.
     * @return array of sql statements
     */
    public function getResetSequenceSQL($table) {

        if ($table instanceof xmldb_table) {
            $tablename = $table->getName();
        } else {
            $tablename = $table;
        }

        // From http://dev.mysql.com/doc/refman/5.0/en/alter-table.html
        $value = (int)$this->mdb->get_field_sql('SELECT MAX(id) FROM {'.$tablename.'}');
        $value++;
        return array("ALTER TABLE $this->prefix$tablename AUTO_INCREMENT = $value");
    }

    /**
     * Calculate proximate row size when using InnoDB
     * tables in Antelope row format.
     *
     * Note: the returned value is a bit higher to compensate for
     *       errors and changes of column data types.
     *
     * @deprecated since Moodle 2.9 MDL-49723 - please do not use this function any more.
     */
    public function guess_antolope_row_size(array $columns) {
        throw new coding_exception('guess_antolope_row_size() can not be used any more, please use guess_antelope_row_size() instead.');
    }

    /**
     * Calculate proximate row size when using InnoDB tables in Antelope row format.
     *
     * Note: the returned value is a bit higher to compensate for errors and changes of column data types.
     *
     * @param xmldb_field[]|database_column_info[] $columns
     * @return int approximate row size in bytes
     */
    public function guess_antelope_row_size(array $columns) {

        if (empty($columns)) {
            return 0;
        }

        $size = 0;
        $first = reset($columns);

        if (count($columns) > 1) {
            // Do not start with zero because we need to cover changes of field types and
            // this calculation is most probably not be accurate.
            $size += 1000;
        }

        if ($first instanceof xmldb_field) {
            foreach ($columns as $field) {
                switch ($field->getType()) {
                    case XMLDB_TYPE_TEXT:
                        $size += 768;
                        break;
                    case XMLDB_TYPE_BINARY:
                        $size += 768;
                        break;
                    case XMLDB_TYPE_CHAR:
                        $bytes = $field->getLength() * 3;
                        if ($bytes > 768) {
                            $bytes = 768;
                        }
                        $size += $bytes;
                        break;
                    default:
                        // Anything else is usually maximum 8 bytes.
                        $size += 8;
                }
            }

        } else if ($first instanceof database_column_info) {
            foreach ($columns as $column) {
                switch ($column->meta_type) {
                    case 'X':
                        $size += 768;
                        break;
                    case 'B':
                        $size += 768;
                        break;
                    case 'C':
                        $bytes = $column->max_length * 3;
                        if ($bytes > 768) {
                            $bytes = 768;
                        }
                        $size += $bytes;
                        break;
                    default:
                        // Anything else is usually maximum 8 bytes.
                        $size += 8;
                }
            }
        }

        return $size;
    }

    /**
     * Given one correct xmldb_table, returns the SQL statements
     * to create it (inside one array).
     *
     * @param xmldb_table $xmldb_table An xmldb_table instance.
     * @return array An array of SQL statements, starting with the table creation SQL followed
     * by any of its comments, indexes and sequence creation SQL statements.
     */
    public function getCreateTableSQL($xmldb_table) {
        // First find out if want some special db engine.
        $engine = $this->mdb->get_dbengine();
        // Do we know collation?
        $collation = $this->mdb->get_dbcollation();

        // Do we need to use compressed format for rows?
        $rowformat = "";
        $size = $this->guess_antelope_row_size($xmldb_table->getFields());
        if ($size > self::ANTELOPE_MAX_ROW_SIZE) {
            if ($this->mdb->is_compressed_row_format_supported()) {
                $rowformat = "\n ROW_FORMAT=Compressed";
            }
        }

        $utf8mb4rowformat = $this->mdb->get_row_format_sql($engine, $collation);
        $rowformat = ($utf8mb4rowformat == '') ? $rowformat : $utf8mb4rowformat;

        $sqlarr = parent::getCreateTableSQL($xmldb_table);

        // This is a very nasty hack that tries to use just one query per created table
        // because MySQL is stupidly slow when modifying empty tables.
        // Note: it is safer to inject everything on new lines because there might be some trailing -- comments.
        $sqls = array();
        $prevcreate = null;
        $matches = null;
        foreach ($sqlarr as $sql) {
            if (preg_match('/^CREATE TABLE ([^ ]+)/', $sql, $matches)) {
                $prevcreate = $matches[1];
                $sql = preg_replace('/\s*\)\s*$/s', '/*keyblock*/)', $sql);
                // Let's inject the extra MySQL tweaks here.
                if ($engine) {
                    $sql .= "\n ENGINE = $engine";
                }
                if ($collation) {
                    if (strpos($collation, 'utf8_') === 0) {
                        $sql .= "\n DEFAULT CHARACTER SET utf8";
                    }
                    $sql .= "\n DEFAULT COLLATE = $collation ";
                }
                if ($rowformat) {
                    $sql .= $rowformat;
                }
                $sqls[] = $sql;
                continue;
            }
            if ($prevcreate) {
                if (preg_match('/^ALTER TABLE '.$prevcreate.' COMMENT=(.*)$/s', $sql, $matches)) {
                    $prev = array_pop($sqls);
                    $prev .= "\n COMMENT=$matches[1]";
                    $sqls[] = $prev;
                    continue;
                }
                if (preg_match('/^CREATE INDEX ([^ ]+) ON '.$prevcreate.' (.*)$/s', $sql, $matches)) {
                    $prev = array_pop($sqls);
                    if (strpos($prev, '/*keyblock*/')) {
                        $prev = str_replace('/*keyblock*/', "\n, KEY $matches[1] $matches[2]/*keyblock*/", $prev);
                        $sqls[] = $prev;
                        continue;
                    } else {
                        $sqls[] = $prev;
                    }
                }
                if (preg_match('/^CREATE UNIQUE INDEX ([^ ]+) ON '.$prevcreate.' (.*)$/s', $sql, $matches)) {
                    $prev = array_pop($sqls);
                    if (strpos($prev, '/*keyblock*/')) {
                        $prev = str_replace('/*keyblock*/', "\n, UNIQUE KEY $matches[1] $matches[2]/*keyblock*/", $prev);
                        $sqls[] = $prev;
                        continue;
                    } else {
                        $sqls[] = $prev;
                    }
                }
            }
            $prevcreate = null;
            $sqls[] = $sql;
        }

        foreach ($sqls as $key => $sql) {
            $sqls[$key] = str_replace('/*keyblock*/', "\n", $sql);
        }

        return $sqls;
    }

    /**
     * Given one xmldb_table and one xmldb_field, return the SQL statements needed to add the field to the table.
     *
     * @param xmldb_table $xmldb_table The table related to $xmldb_field.
     * @param xmldb_field $xmldb_field The instance of xmldb_field to create the SQL from.
     * @param string $skip_type_clause The type clause on alter columns, NULL by default.
     * @param string $skip_default_clause The default clause on alter columns, NULL by default.
     * @param string $skip_notnull_clause The null/notnull clause on alter columns, NULL by default.
     * @return array The SQL statement for adding a field to the table.
     */
    public function getAddFieldSQL($xmldb_table, $xmldb_field, $skip_type_clause = NULL, $skip_default_clause = NULL, $skip_notnull_clause = NULL) {
        $sqls = parent::getAddFieldSQL($xmldb_table, $xmldb_field, $skip_type_clause, $skip_default_clause, $skip_notnull_clause);

        if ($this->table_exists($xmldb_table)) {
            $tablename = $xmldb_table->getName();

            $size = $this->guess_antelope_row_size($this->mdb->get_columns($tablename));
            $size += $this->guess_antelope_row_size(array($xmldb_field));

            if ($size > self::ANTELOPE_MAX_ROW_SIZE) {
                if ($this->mdb->is_compressed_row_format_supported()) {
                    $format = strtolower($this->mdb->get_row_format($tablename));
                    if ($format === 'compact' or $format === 'redundant') {
                        // Change the format before conversion so that we do not run out of space.
                        array_unshift($sqls, "ALTER TABLE {$this->prefix}$tablename ROW_FORMAT=Compressed");
                    }
                }
            }
        }

        return $sqls;
    }

    public function getAlterFieldSQL($xmldb_table, $xmldb_field, $skip_type_clause = NULL, $skip_default_clause = NULL, $skip_notnull_clause = NULL)
    {
        $tablename = $xmldb_table->getName();
        $dbcolumnsinfo = $this->mdb->get_columns($tablename);

        if (($this->mdb->has_breaking_change_sqlmode()) &&
            ($dbcolumnsinfo[$xmldb_field->getName()]->meta_type == 'X') &&
            ($xmldb_field->getType() == XMLDB_TYPE_INTEGER)) {
            // Ignore 1292 ER_TRUNCATED_WRONG_VALUE Truncated incorrect INTEGER value: '%s'.
            $altercolumnsqlorig = $this->alter_column_sql;
            $this->alter_column_sql = str_replace('ALTER TABLE', 'ALTER IGNORE TABLE', $this->alter_column_sql);
            $result = parent::getAlterFieldSQL($xmldb_table, $xmldb_field, $skip_type_clause, $skip_default_clause, $skip_notnull_clause);
            // Restore the original ALTER SQL statement pattern.
            $this->alter_column_sql = $altercolumnsqlorig;

            return $result;
        }

        return parent::getAlterFieldSQL($xmldb_table, $xmldb_field, $skip_type_clause, $skip_default_clause, $skip_notnull_clause);
    }

    /**
     * Given one correct xmldb_table, returns the SQL statements
     * to create temporary table (inside one array).
     *
     * @param xmldb_table $xmldb_table The xmldb_table object instance.
     * @return array of sql statements
     */
    public function getCreateTempTableSQL($xmldb_table) {
        // Do we know collation?
        $collation = $this->mdb->get_dbcollation();
        $this->temptables->add_temptable($xmldb_table->getName());

        $sqlarr = parent::getCreateTableSQL($xmldb_table);

        // Let's inject the extra MySQL tweaks.
        foreach ($sqlarr as $i=>$sql) {
            if (strpos($sql, 'CREATE TABLE ') === 0) {
                // We do not want the engine hack included in create table SQL.
                $sqlarr[$i] = preg_replace('/^CREATE TABLE (.*)/s', 'CREATE TEMPORARY TABLE $1', $sql);
                if ($collation) {
                    if (strpos($collation, 'utf8_') === 0) {
                        $sqlarr[$i] .= " DEFAULT CHARACTER SET utf8";
                    }
                    $sqlarr[$i] .= " DEFAULT COLLATE $collation ROW_FORMAT=DYNAMIC";
                }
            }
        }

        return $sqlarr;
    }

    /**
     * Given one correct xmldb_table, returns the SQL statements
     * to drop it (inside one array).
     *
     * @param xmldb_table $xmldb_table The table to drop.
     * @return array SQL statement(s) for dropping the specified table.
     */
    public function getDropTableSQL($xmldb_table) {
        $sqlarr = parent::getDropTableSQL($xmldb_table);
        if ($this->temptables->is_temptable($xmldb_table->getName())) {
            $sqlarr = preg_replace('/^DROP TABLE/', "DROP TEMPORARY TABLE", $sqlarr);
        }
        return $sqlarr;
    }

    /**
     * Given one XMLDB Type, length and decimals, returns the DB proper SQL type.
     *
     * @param int $xmldb_type The xmldb_type defined constant. XMLDB_TYPE_INTEGER and other XMLDB_TYPE_* constants.
     * @param int $xmldb_length The length of that data type.
     * @param int $xmldb_decimals The decimal places of precision of the data type.
     * @return string The DB defined data type.
     */
    public function getTypeSQL($xmldb_type, $xmldb_length=null, $xmldb_decimals=null) {

        switch ($xmldb_type) {
            case XMLDB_TYPE_INTEGER:    // From http://mysql.com/doc/refman/5.0/en/numeric-types.html!
                if (empty($xmldb_length)) {
                    $xmldb_length = 10;
                }
                if ($xmldb_length > 9) {
                    $dbtype = 'BIGINT';
                } else if ($xmldb_length > 6) {
                    $dbtype = 'INT';
                } else if ($xmldb_length > 4) {
                    $dbtype = 'MEDIUMINT';
                } else if ($xmldb_length > 2) {
                    $dbtype = 'SMALLINT';
                } else {
                    $dbtype = 'TINYINT';
                }
                $dbtype .= '(' . $xmldb_length . ')';
                break;
            case XMLDB_TYPE_NUMBER:
                $dbtype = $this->number_type;
                if (!empty($xmldb_length)) {
                    $dbtype .= '(' . $xmldb_length;
                    if (!empty($xmldb_decimals)) {
                        $dbtype .= ',' . $xmldb_decimals;
                    }
                    $dbtype .= ')';
                }
                break;
            case XMLDB_TYPE_FLOAT:
                $dbtype = 'DOUBLE';
                if (!empty($xmldb_decimals)) {
                    if ($xmldb_decimals < 6) {
                        $dbtype = 'FLOAT';
                    }
                }
                if (!empty($xmldb_length)) {
                    $dbtype .= '(' . $xmldb_length;
                    if (!empty($xmldb_decimals)) {
                        $dbtype .= ',' . $xmldb_decimals;
                    } else {
                        $dbtype .= ', 0'; // In MySQL, if length is specified, decimals are mandatory for FLOATs
                    }
                    $dbtype .= ')';
                }
                break;
            case XMLDB_TYPE_CHAR:
                $dbtype = 'VARCHAR';
                if (empty($xmldb_length)) {
                    $xmldb_length='255';
                }
                $dbtype .= '(' . $xmldb_length . ')';
                if ($collation = $this->mdb->get_dbcollation()) {
                    if (strpos($collation, 'utf8_') === 0) {
                        $dbtype .= " CHARACTER SET utf8";
                    }
                    $dbtype .= " COLLATE $collation";
                }
                break;
            case XMLDB_TYPE_TEXT:
                $dbtype = 'LONGTEXT';
                if ($collation = $this->mdb->get_dbcollation()) {
                    if (strpos($collation, 'utf8_') === 0) {
                        $dbtype .= " CHARACTER SET utf8";
                    }
                    $dbtype .= " COLLATE $collation";
                }
                break;
            case XMLDB_TYPE_BINARY:
                $dbtype = 'LONGBLOB';
                break;
            case XMLDB_TYPE_DATETIME:
                $dbtype = 'DATETIME';
        }
        return $dbtype;
    }

    /**
     * Given one xmldb_table and one xmldb_field, return the SQL statements needed to add its default
     * (usually invoked from getModifyDefaultSQL()
     *
     * @param xmldb_table $xmldb_table The xmldb_table object instance.
     * @param xmldb_field $xmldb_field The xmldb_field object instance.
     * @return array Array of SQL statements to create a field's default.
     */
    public function getCreateDefaultSQL($xmldb_table, $xmldb_field) {
        // Just a wrapper over the getAlterFieldSQL() function for MySQL that
        // is capable of handling defaults
        return $this->getAlterFieldSQL($xmldb_table, $xmldb_field);
    }

    /**
     * Given one correct xmldb_field and the new name, returns the SQL statements
     * to rename it (inside one array).
     *
     * @param xmldb_table $xmldb_table The table related to $xmldb_field.
     * @param xmldb_field $xmldb_field The instance of xmldb_field to get the renamed field from.
     * @param string $newname The new name to rename the field to.
     * @return array The SQL statements for renaming the field.
     */
    public function getRenameFieldSQL($xmldb_table, $xmldb_field, $newname) {
        // NOTE: MySQL is pretty different from the standard to justify this overloading.

        // Need a clone of xmldb_field to perform the change leaving original unmodified
        $xmldb_field_clone = clone($xmldb_field);

        // Change the name of the field to perform the change
        $xmldb_field_clone->setName($newname);

        $fieldsql = $this->getFieldSQL($xmldb_table, $xmldb_field_clone);

        $sql = 'ALTER TABLE ' . $this->getTableName($xmldb_table) . ' CHANGE ' .
               $this->getEncQuoted($xmldb_field->getName()) . ' ' . $fieldsql;

        return array($sql);
    }

    /**
     * Given one xmldb_table and one xmldb_field, return the SQL statements needed to drop its default
     * (usually invoked from getModifyDefaultSQL()
     *
     * Note that this method may be dropped in future.
     *
     * @param xmldb_table $xmldb_table The xmldb_table object instance.
     * @param xmldb_field $xmldb_field The xmldb_field object instance.
     * @return array Array of SQL statements to create a field's default.
     *
     * @todo MDL-31147 Moodle 2.1 - Drop getDropDefaultSQL()
     */
    public function getDropDefaultSQL($xmldb_table, $xmldb_field) {
        // Just a wrapper over the getAlterFieldSQL() function for MySQL that
        // is capable of handling defaults
        return $this->getAlterFieldSQL($xmldb_table, $xmldb_field);
    }

    /**
     * Returns the code (array of statements) needed to add one comment to the table.
     *
     * @param xmldb_table $xmldb_table The xmldb_table object instance.
     * @return array Array of SQL statements to add one comment to the table.
     */
    function getCommentSQL ($xmldb_table) {
        $comment = '';

        if ($xmldb_table->getComment()) {
            $comment .= 'ALTER TABLE ' . $this->getTableName($xmldb_table);
            $comment .= " COMMENT='" . $this->addslashes(substr($xmldb_table->getComment(), 0, 60)) . "'";
        }
        return array($comment);
    }

    /**
     * Given one object name and it's type (pk, uk, fk, ck, ix, uix, seq, trg).
     *
     * (MySQL requires the whole xmldb_table object to be specified, so we add it always)
     *
     * This is invoked from getNameForObject().
     * Only some DB have this implemented.
     *
     * @param string $object_name The object's name to check for.
     * @param string $type The object's type (pk, uk, fk, ck, ix, uix, seq, trg).
     * @param string $table_name The table's name to check in
     * @return bool If such name is currently in use (true) or no (false)
     */
    public function isNameInUse($object_name, $type, $table_name) {

        switch($type) {
            case 'ix':
            case 'uix':
                // First of all, check table exists
                $metatables = $this->mdb->get_tables();
                if (isset($metatables[$table_name])) {
                    // Fetch all the indexes in the table
                    if ($indexes = $this->mdb->get_indexes($table_name)) {
                        // Look for existing index in array
                        if (isset($indexes[$object_name])) {
                            return true;
                        }
                    }
                }
                break;
        }
        return false; //No name in use found
    }


    /**
     * Returns an array of reserved words (lowercase) for this DB
     * @return array An array of database specific reserved words
     */
    public static function getReservedWords() {
        // This file contains the reserved words for MySQL databases.
        $reserved_words = array (
            // From http://dev.mysql.com/doc/refman/6.0/en/reserved-words.html.
            'accessible', 'add', 'all', 'alter', 'analyze', 'and', 'as', 'asc',
            'asensitive', 'before', 'between', 'bigint', 'binary',
            'blob', 'both', 'by', 'call', 'cascade', 'case', 'change',
            'char', 'character', 'check', 'collate', 'column',
            'condition', 'connection', 'constraint', 'continue',
            'convert', 'create', 'cross', 'current_date', 'current_time',
            'current_timestamp', 'current_user', 'cursor', 'database',
            'databases', 'day_hour', 'day_microsecond',
            'day_minute', 'day_second', 'dec', 'decimal', 'declare',
            'default', 'delayed', 'delete', 'desc', 'describe',
            'deterministic', 'distinct', 'distinctrow', 'div', 'double',
            'drop', 'dual', 'each', 'else', 'elseif', 'enclosed', 'escaped',
            'exists', 'exit', 'explain', 'false', 'fetch', 'float', 'float4',
            'float8', 'for', 'force', 'foreign', 'from', 'fulltext', 'grant',
            'group', 'having', 'high_priority', 'hour_microsecond',
            'hour_minute', 'hour_second', 'if', 'ignore', 'in', 'index',
            'infile', 'inner', 'inout', 'insensitive', 'insert', 'int', 'int1',
            'int2', 'int3', 'int4', 'int8', 'integer', 'interval', 'into', 'is',
            'iterate', 'join', 'key', 'keys', 'kill', 'leading', 'leave', 'left',
            'like', 'limit', 'linear', 'lines', 'load', 'localtime', 'localtimestamp',
            'lock', 'long', 'longblob', 'longtext', 'loop', 'low_priority', 'master_heartbeat_period',
            'master_ssl_verify_server_cert', 'match', 'mediumblob', 'mediumint', 'mediumtext',
            'middleint', 'minute_microsecond', 'minute_second',
            'mod', 'modifies', 'natural', 'not', 'no_write_to_binlog',
            'null', 'numeric', 'on', 'optimize', 'option', 'optionally',
            'or', 'order', 'out', 'outer', 'outfile', 'overwrite', 'precision', 'primary',
            'procedure', 'purge', 'raid0', 'range', 'read', 'read_only', 'read_write', 'reads', 'real',
            'references', 'regexp', 'release', 'rename', 'repeat', 'replace',
            'require', 'restrict', 'return', 'revoke', 'right', 'rlike', 'schema',
            'schemas', 'second_microsecond', 'select', 'sensitive',
            'separator', 'set', 'show', 'smallint', 'soname', 'spatial',
            'specific', 'sql', 'sqlexception', 'sqlstate', 'sqlwarning',
            'sql_big_result', 'sql_calc_found_rows', 'sql_small_result',
            'ssl', 'starting', 'straight_join', 'table', 'terminated', 'then',
            'tinyblob', 'tinyint', 'tinytext', 'to', 'trailing', 'trigger', 'true',
            'undo', 'union', 'unique', 'unlock', 'unsigned', 'update',
            'upgrade', 'usage', 'use', 'using', 'utc_date', 'utc_time',
            'utc_timestamp', 'values', 'varbinary', 'varchar', 'varcharacter',
            'varying', 'when', 'where', 'while', 'with', 'write', 'x509',
            'xor', 'year_month', 'zerofill',
            // Added in MySQL 8.0, compared to MySQL 5.7:
            // https://dev.mysql.com/doc/refman/8.0/en/keywords.html#keywords-new-in-current-series.
            '_filename', 'admin', 'cume_dist', 'dense_rank', 'empty', 'except', 'first_value', 'grouping', 'groups',
            'json_table', 'lag', 'last_value', 'lead', 'nth_value', 'ntile',
            'of', 'over', 'percent_rank', 'persist', 'persist_only', 'rank', 'recursive', 'row_number',
            'system', 'window'
        );
        return $reserved_words;
    }
}
